An ignition system for gas turbine engines is shown and described in U.S. Pat. No. 3,731,143 issued May 1, 1973 and assigned to the same assignee as the present application. The ignition system described therein has a high energy output capability at low input voltage. While the circuit works well, there is a possibility of semiconductor failure under igniter load conditions, such as open circuit, short circuit and flame impingement. Experience has shown that it is difficult to design satisfactory inductive ignition circuits using semiconductors which will operate under igniter plug load conditions mentioned above. Failures occur due to excessive junction temperatures generated during the igniter load variations.
In order to overcome this problem, U.S. Pat. No. 3,835,350, issued Sept. 10, 1974 and assigned to the same assignee as the present application, uses a capacitor in parallel with the spark discharge device connected across the secondary winding of the high voltage transformer so that in case of an open circuit across the spark discharge device the capacitor dissipates most of the energy in the secondary circuit instead of the energy being dissipated in the primary circuit with resultant damage to the switching semiconductor and other components therein. However, the capacitor required for this purpose is expensive to manufacture and substantially increases the cost of the ignition circuit.